1. Field of the Invention
The present invention relates to tendon tensioning anchor assemblies, and more particularly to improvements in sealing post-tension anchor assemblies to protect the exposed portions of a tendon from corrosion.
2. Description of the Prior Art
Conventional concrete reinforcing using tendons for stressing typically includes a pair of anchor assemblies mounted in spaced apart relation with an elongated reinforcing tendon extending therebetween. The tendon is placed under an axial load, either by pretensioning or post-tensioning, and connected to the concrete in the tensioned condition by the anchor assemblies. Tensioning of the tendon after the formation and setting of the concrete structure is known as post-tensioning and is widely used in the construction of prestressed concrete structures.
In the course of installing a tendon tensioning anchor assembly in a concrete structure, a hydraulic jack or the like is releasably attached to an exposed extending end of the tendon to apply a predetermined amount of tension to the tendon. The sheath, within which the remainder of the tendon is enclosed, protects against moisture and isolates the tendon from the surrounding concrete to facilitate the movement of the tendon relative to the surrounding concrete. When the desired amount of tension is applied to the tendon, wedges, threaded nuts or the like are used to connect the tendon to the anchor to hold the tendon in a stressed condition. After tensioning, the recessed ends of the tendon are cut off at the anchor by use of a cutting torch or the like.
Moisture travels through concrete. Concrete structures are frequently exposed to corrosive elements, such as de-icing chemicals, sea water, salt air or brackish water. In some environments, ground, water, run-off, snow and the like can immerse portions of the slab for substantial periods of time. The exposed ends of tendons from which the waterproof sheath has been stripped for tensioning can represent a substantial potential corrosion problem. Unless sealed against moisture, the exposed portions of the tendon are likely to suffer corrosion. This not only weakening the tendon, but the by-products of the corrosive reaction can fracture the surrounding structure.
One method of protecting tendons is disclosed in U.S. Pat. No. 4,348,844 issued to Schupack et al on Sept. 14, 1982. According to the teachings of this patent, the entire anchor assembly is enclosed in a housing or envelope. The use of a housing enclosing the entire anchor assembly is unduly expensive and is subject to damage during the cutting of the exposed recessed tendon end by use of a cutting torch. Installation of the housing as a separate unit apart from the anchor plate assembly, is time consuming and costly. This increased cost is unnecessary because there is no need to protect the entire anchor plate assembly from corrosion so long as the tendon itself is protected. Further, this assembly relies on plastic threads to form the seal. The manufacturing tolerances, dirty environment, distortion from heat and potential for stress deformation can result in a less than a reliable seal arrangement. Other examples of anchor assemblies using unreliable pleastic thread seals and/or multiple parts are shown in U.S. Pat. Nos. 4,616,458, 4,343,122, 3,956,797 and 3,820,832 and the U.S. and foreign patents cited in these U.S. patents.
The U.S. Pat. No. 3,596,330, to Scott, discloses another method which uses a deformable plug pushed into place to form a seal. However, no means are provided for positively locking the seal in position to prevent it from being dislodged during grouting.